The Proton Transfer Reaction-Mass Spectrometer for Atmospheric Chemistry Tracers of
Diesel Exhaust Emissions and Measurements of Trace gas and Aerosol properties.
Debra Garvey, Matt Erickson and Tom Jobson
Laboratory for Atmospheric Research
Department of Civil and Environmental Engineering
Objectives
Introduction
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Diesel exhaust experiment
It has previously been difficult to identify the emissions of diesel
exhaust until the use of a technique referred to as the
Dynamic Dilution System. The use of a Proton Transfer ReactionMass Spectrometer(PTR-MS) was vital during the experiment
because the reagent ion, H3O+ , is highly reactive with organic
compounds such as alkanes which are present in diesel exhaust
emissions. The reaction which takes place is that the organic
compound, R, would be protonated by the reagent ion and a mass
reading plus one would be the result and it was expected that the
new compound would dissociate into masses differing by fourteen
which would represent a CH2. The alkanes used during the
experiment ranged from lengths of six through seventeen carbons.
Also Nitrogen gas was a necessity because the alkanes would react
quickly with air, hence their ability to cause air pollution. The
main purpose of the experiment was to determine the reaction
time and to make sure that the sensitivity of the technique is high
enough to detect different compounds in a complex mixture such
as diesel exhaust.
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
The reaction rate is the speed at which molecules collide
and thus react with each other. For this technique the
reaction time must be fast enough so that molecules react
proving that the procedure is reliable.
A high reaction rate displays the sensitivity of the
instrument which is vital in the research of diesel exhaust
emissions.
During CABINEX, it is expected that with the emission of
isoprene there would be a similar pattern with the
production of formaldehyde and other air pollutants.
To successfully detect and quantify the biogenic
emissions, and the products which are formed,
throughout a time period.
Experiment
Apparatus
Liquid N2 Tank
Cole Parmer Hamilton Rotameter (Liters per minute)
Copper Pipeline
Insulation: Glass wool and foil
Clamps
Heat suppliers: Heating tapes and ropes and variable
autotransformers
Septa
Hamilton Syringe (50 uL)
Harvard Apparatus PHP 2000 Infusion Syringe pump (20 uL/hr)
Thermometers (Centigrade)
Ionicon Analytik Proton Transfer Reaction-Mass Spectrometer
(PTR-MS)
Rotameter (LPM)
PTR-MS
MACL
Measurement of Trace Gas and Aerosol Properties
Trees are known to release biogenic compounds and among them
are isoprene, C5H8. Isoprene is released from trees during
photosynthesis with high intensities of sunlight. The isoprene in
turn reacts with the hydroxyl radicals, OH, present in the
atmosphere. From this reaction a host of compounds which
cause air pollution, such as formaldehyde, are produced. The
purpose of the PTR-MS is to detect the increase and decrease of
isoprene over time with the difference of sunlight intensity. It is
expected that the measurements of formaldehyde should follow
the signal reading of isoprene just not as intense. This experiment
was conducted at the University of Michigan Biological Station
during CABINEX using the Mobile Atmospheric Chemistry
Laboratory(MACL).
The alkanes have
this appearance
due to their PA >
PA of H2O and so
they are easily
detected. Hence
why as their size
increases so do
their sum of ion
signals.
Below is the comparison of the PTR-MS with that of the
electron ionization mass spectrum of Tetradecane.
Insulated Pipeline
N2
Gas
CABINEX Tower and trailer inlet.
Results and Discussion
In this figure the
PTR-MS detected
monoterpenes at
the expected
masses of 137 and 81
amu.
Syringe Pump
Constant heat and
insulation
Procedure
The N2 gas was supplied through the apparatus at a constant
flow of 25 LPM and the alkane was injected through the system at
20 uL/hr.
The alkanes were kept at a temperature of approximately 90 C or
30 C, for it was dependent upon their polarity and the required
heat supply for sufficient signals.
The pipeline required constant heat to prevent condensation
which would increase dark counts on the PTR-MS signal readings.
Each cycle was 120 seconds and the counts per second (cps)
were recorded for each interest peak.
After a number of cycles with stable readings, the next alkane
was injected into the system.
The long chain alkanes were injected at a mixing ratio of
approximately 2ppmv while the smaller alkanes were injected at a
higher concentration of ~3ppmv.
Clearly the PTR-MS
data demonstrates
the production of
VOCs from the
reaction of biogenic
emissions with the
atmosphere during
moments of intense
sunlight.
Conclusion:
The sensitivity of the PTR-MS to the alkanes is efficient to detect
the alkanes with a fast reaction time which is greatly important for
gas phase emissions due to their ability to quickly react with the
atmosphere. The VOCs detected by the PTR-MS also included
acetaldehyde , MEK, PAN and multiple species to name a few.
Acknowledgements:
NSF REU program grant number 0754990, University Of Michigan
Biological Station.